1. Field of the Invention
The present invention relates to foamed well cementing compositions and methods, and more particularly, to such compositions and methods which are particularly suitable for use in salt containing subterranean environments.
2. Description of the Prior Art
In cementing operations performed in oil and gas wells, a hydraulic cement composition is pumped down the well bore penetrating a subterranean formation into contact with the formation and allowed to set therein. Such cementing operations generally involve either primary cementing or squeeze cementing. In performing a primary cementing operation, the cement composition is pumped through a conduit disposed in the well bore and back up through the annulus between the conduit and the earth formations forming the sides of the well bore. Upon setting, the cement composition bonds to the conduit and to the sides of the well bore whereby the conduit is rigidly supported within the well bore, and fluid movement in the annulus between the conduit and the sides of the well bore is prevented. In squeeze cementing operations, a hydraulic cement composition is pumped through the well bore into a particular subterranean formation or zone therein from which it is desired to stop the flow of undesirable fluids. Upon setting, the cement composition bonds to the formation whereby fluids are prevented from flowing therefrom into the well bore.
When the above described cementing operations are carried out in subterranean formations comprised of salt, i.e., alkali metal or alkaline earth metal salts, it has been found that good bonding between the salt formation and cement compositions is most often achieved when the cement compositions are formed with water containing salt, i.e., salt concentrations of from about 18% by weight of water to saturation. In addition, the salt functions in the cement compositions as a dispersant and can cause the cement compositions to expand upon setting whereby bonding and sealing are enhanced.
Foamed cement compositions have heretofore been used in performing oil and gas well cementing operations. Foamed cement compositions are advantageous in that they have low densities and low fluid loss properties. In addition, as described in U.S. Pat. No. 4,340,427 issued Jul. 20, 1982, foamed cement compositions have an increased compressibility as compared to non-foamed cement compositions. The increased compressibility helps prevent the incursion of pressurized formation gas into and around the cement composition prior to when it sets.
While heretofore used foamed cement compositions have included various foam stabilizers for preventing the compositions from prematurely separating into their slurry and gas components, when the water utilized contains high salt concentrations (typically above about 18%), the times required for the cement compositions to set are extended. In addition, the use of conventional foam stabilizers in foamed salt water cement compositions disadvantageously extend the set times even further. However, cement compositions which are formed with salt water have been found to be particularly suitable for carrying out cementing operations in subterranean well formations comprised or partially comprised of salt. That is, salt containing cement compositions form a stronger bond to salt containing formations than do fresh water cement compositions. Thus, salt water cement compositions, and particularly light weight foamed salt water cement compositions, are useful in performing cementing operations in salt containing subterranean formations, but the long set times of such cement compositions has heretofore been disadvantageous.
By the present invention, improved foamed cement compositions for performing cementing operations in salt containing subterranean formation environments and methods of performing cementing operations using the compositions are provided.